Multiple chemical sensitivity
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Multiple chemical sensitivity (MCS), also known as idiopathic environmental intolerances (IEI), is an unrecognized diagnosis characterized by chronic symptoms attributed to exposure to commonly used chemicals. Symptoms are typically vague and non-specific. They may include fatigue, headaches, nausea, and dizziness. Although these symptoms can be debilitating, MCS is not recognized as an organic, chemical-caused illness by the World Health Organization, American Medical Association, or any of several other professional medical organizations. Blinded clinical trials show that people with MCS react as often and as strongly to placebos as they do to chemical stimuli; the existence and severity of symptoms is related to perception that a chemical stimulus is present. Some attribute the symptoms to depression, somatoform disorders, or anxiety disorders.
There is a lack of agreement among MCS researchers on the cause or causes of the condition. A 2018 systematic review concluded that the evidence suggests that abnormalities in sensory processing pathways combined with peculiar personality traits best explains this condition.
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America. "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES/MCS."
Neuro-imaging suggests that people claiming MCS may have neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the autonomic nervous system areas. These abnormalities have been documented both in studies using PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) scans.
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies. Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.
In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction. While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients. As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.
More recently, a French study found that subjects with MCS had higher levels of histamine than controls. It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.
Several mechanisms for a psychological etiology of the condition have been proposed, including theories based on misdiagnoses of an underlying mental illness, stress, or classical conditioning. Many people with MCS also meet the criteria for major depressive disorder or anxiety disorder.[non-primary source needed] Other proposed explanations include somatic symptom disorder,[non-primary source needed] panic disorder,[non-primary source needed] migraine, chronic fatigue syndrome, or fibromyalgia and brain fog. Through behavioral conditioning, it has been proposed that people with MCS may develop real, but unintentionally psychologically produced, symptoms, such as anticipatory nausea, when they encounter certain odors or other perceived triggers.[non-primary source needed] It has also been proposed in one study that individuals may have a tendency to "catastrophically misinterpret benign physical symptoms"[non-primary source needed] or simply have a disturbingly acute sense of smell.[medical citation needed] The personality trait absorption, in which individuals are predisposed to becoming deeply immersed in sensory experiences, may be stronger in individuals reporting symptoms of MCS.[non-primary source needed] In the 1990s, behaviors exhibited by MCS sufferers were hypothesized by some to reflect broader sociological fears about industrial pollution and broader societal trends of technophobia and chemophobia.
In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department.
Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA. They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.
Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls, including polymorphisms and differences in expression of the following: CYP2D6, NAT2, GSTM1, and PON1 and PON2.
International Classification of Diseases
The International Statistical Classification of Diseases and Related Health Problems (ICD), maintained by the World Health Organization, does not recognize multiple chemical sensitivity or environmental sensitivity as a discrete disease. The American Academy of Allergy, Asthma, and Immunology, the California Medical Association, the American College of Physicians, and the International Society of Regulatory Toxicology and Pharmacology also do not recognize MCS. The US Occupational Safety and Health Administration (OSHA) indicates that MCS is highly controversial and that there is insufficient scientific evidence to explain the relationship between the suggested causes of MCS and its symptoms. OSHA recommends evaluation by a physician knowledgeable of the symptoms presented.
In line with the lack of consensus that MCS has any physiological cause, there is no current clinically proven treatment for MCS. It has been suggested that a multidisciplinary approach be taken to treating this condition taking into account, peculiar personality traits often seen in affected individuals and physiological abnormalities in sensorary pathways and the limbic system. There is also no scientific consensus on supportive therapies for MCS, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."
There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS. And some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.
The most extensive epidemiological study into MCS in the United States was in 2005. It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.
In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.
While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9 per cent reported having adverse reactions to multiple chemicals. The study also found that for 55.4 per cent of those with MCS, the symptoms triggered by chemical exposures could be disabling.
Gulf War syndrome
Veterans of the Gulf War attributed to Gulf War syndrome are similar to those reported for MCS, including headache, fatigue, muscle stiffness, joint pain, inability to concentrate, sleep problems, and gastrointestinal issues.
A population-based, cross-sectional epidemiological study involving American veterans of the Gulf War, non-Gulf War veterans, and non-deployed reservists enlisted both during Gulf War era and outside the Gulf War era concluded the prevalence of MCS-type symptoms in Gulf War veterans was somewhat higher than in non-Gulf War veterans. After adjusting for potentially confounding factors (age, sex, and military training), there was a robust association between individuals with MCS-type symptoms and psychiatric treatment (either therapy or medication) before deployment and, therefore, before any possible deployment-connected chemical exposures.
The odds of reporting MCS or chronic multiple-symptom illness was 3.5 times greater for Gulf War veterans than non-Gulf veterans. Gulf War veterans have an increased rate of being diagnosed with multiple-symptom conditions compared to military personnel deployed to other conflicts.
MCS was first proposed as a distinct disease by Theron G. Randolph in 1950. In 1965, Randolph founded the Society for Clinical Ecology as an organization to promote his ideas about symptoms reported by his patients. As a consequence, clinical ecology emerged as a non-recognized medical specialty. In 1984, the Society for Clinical Ecology changed its name to American Academy of Environmental Medicine (AAEM). In the 1990s, an association was noted with chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome.
In 1994, the AMA, American Lung Association, US EPA and the US Consumer Product Safety Commission published a booklet on indoor air pollution that discusses MCS, among other issues. The booklet further states that a pathogenesis of MCS has not been definitively proven, and that symptoms that have been self-diagnosed by a patient as related to MCS could actually be related to allergies or have a psychological basis, and recommends that physicians should counsel patients seeking relief from their symptoms that they may benefit from consultation with specialists in these fields.
In 1995, an Interagency Workgroup on Multiple Chemical Sensitivity was formed under the supervision of the Environmental Health Policy Committee within the United States Department of Health and Human Services to examine the body of research that had been conducted on MCS to that date. The work group included representatives from the Centers for Disease Control and Prevention, United States Environmental Protection Agency, United States Department of Energy, Agency for Toxic Substances and Disease Registry, and the National Institutes of Health. The Predecisional Draft document generated by the workgroup in 1998 recommended additional research in the basic epidemiology of MCS, the performance of case-comparison and challenge studies, and the development of a case definition for MCS. However, the workgroup also concluded that it was unlikely that MCS would receive extensive financial resources from federal agencies because of budgetary constraints and the allocation of funds to other, extensively overlapping syndromes with unknown cause, such as chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome. The Environmental Health Policy Committee is currently inactive, and the workgroup document has not been finalized.
- Electromagnetic hypersensitivity
- Sick building syndrome
- Sensory processing disorder
- Sensory processing sensitivity
- List of questionable diseases
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[D]efinition of the phenomenon is elusive and its pathogenesis as a distinct entity is not confirmed....The current consensus is that in cases of claimed or suspected MCS, complaints should not be dismissed as psychogenic, and a thorough workup is essential. Primary care givers should determine that the individual does not have an underlying physiological problem and should consider the value of consultation with allergists and other specialists.
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